The present invention relates to a malfunction test apparatus for a fuel vapor purge system used in an internal combustion engine of a vehicle such as an automobile.
Fuel vapor purge systems for sending fuel vapor in a fuel tank to an intake passage have been proposed. Specifically, a fuel vapor purge system collects fuel vapor in a fuel tank to a canister and purges the collected fuel vapor to the intake passage as necessary to prevent fuel vapor from being emitted to the atmosphere. Such a purge system includes a canister, a fuel vapor passage and a vapor line. The canister collects fuel vapor in the fuel tank. The fuel vapor passage connects the fuel tank with the canister. The purge line connects the canister with an intake passage. A purge control valve is located in the purge line to adjust the opening size of the purge line. The canister has an atmospheric control valve, through which the canister is selectively exposed to the atmosphere.
When there is a puncture in piping or when a pipe is dislocated, fuel vapor is emitted into the atmosphere from the canister and the fuel tank. Preferably, such leakage is automatically discovered.
Therefore, a leakage test system that differentiates the pressure in a purge system from the outside pressure of the exterior and monitors changes of the purge system pressure has been introduced. For example, the system exposes the interior of the purge system to the negative pressure in an intake system of an engine and closes inlet and outlet passages to seal the purge system. Then, the system monitors changes of the internal pressure of the purge system.
When testing the purge line, the pressure in the purge line is lowered to a negative pressure and changes in the pressure are monitored. To test the purge system, the amount of fuel vapor needs to be in a certain range. If the amount of fuel vapor is out of the range, it cannot be judged whether an increase in the pressure in the purge line is due to atmospheric pressure introduced through puncture or to an excessive amount of fuel vapor.
Japanese Unexamined Patent Publication No. 6-74104 discloses a purge system, n which a canister is constantly connected to the interior f a fuel tank. When diagnosing the system, inlets and out Lets must be closed by valves to seal the purge line to measure the amount of fuel vapor in the system. Thus, purging must be stopped when measuring the amount of fuel vapor, which decreases the amount of purged fuel vapor. The purged fuel vapor may therefore be insufficient.
Accordingly, it is an objective of the present invention to provide a malfunction test apparatus for fuel vapor purge systems that shortens time required for testing and improves the purging effectiveness.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a malfunction test apparatus for a fuel vapor purge system is provided. The apparatus includes a purge system and testing means. The purge system connects a fuel tank with a canister and collects fuel vapor generated in the fuel tank in the canister. The purge system purges the collected fuel vapor to an intake passage of an internal combustion engine through a purge passage. The purge passage includes the fuel tank. The testing means seals the purge passage and measures a change of pressure due to fuel vapor generation in the fuel tank. The testing means measures a rate of change of the pressure in the purge passage after differentiating the pressure in the purge passage from the pressure outside the purge passage and after sealing the purge passage. The testing means determines whether there is a leak in the purge passage based on the change of pressure due to fuel vapor generation and on the measured rate of change of the pressure in the purge passage. After measuring the change of pressure due to fuel vapor generation, the testing means determines that there is a leak in the purge passage only if the change of pressure due to fuel vapor generation satisfies a predetermined condition.
The present invention may also be embodied in a method for determining whether a malfunction has occurred in a fuel vapor purge system. The purge system connects a fuel tank with a canister and collects fuel vapor generated in the fuel tank by the canister. The purge system purges the collected fuel vapor to an intake passage of an internal combustion engine through a purge passage. The purge passage includes the fuel tank. The method includes measuring a change of pressure due to fuel vapor generation in the fuel tank while sealing the purge passage, and determining whether there is a leak in the purge passage based on the change of pressure due to fuel vapor generation and based on the rate at which the pressure in the purge passage approaches atmospheric pressure when the purge passage is sealed.